Re: [PATCH v2 0/5] LoongArch: Add kernel relocation and KASLR support

[Youling Tang]

On 02/08/2023 04:27 PM, Xi Ruoyao wrote:
> On Wed, 2023-02-08 at 12:37 +0800, Youling Tang wrote:
> > In the case of "[Patch v2 2/5] LoongArch: use la.pcrel instenad of
> > la.abs for exception handlerS", the above failure will occur.
> >
> > Patch2 may have certain problems when using the old toolchains.
> >
> > Youling.
>
> Thanks for the test...
>
> The problem is: old toolchain uses pcaddu12i/ori/lu32i.d/lu52i.d/add.d
> for a 3-operand la.pcrel, while the new toolchain uses
> pcalau12i/addi.d/lu32i/lu52i/add.d.  (I've somehow forgotten all the
> difference!)
>
> We can fix it with something like...
>
> > +void reloc_handler(unsigned long handler, struct handler_reloc *rel)
> > +{
> > +	if (!rel)
> > +		return;
> > +
> > +	for (unsigned long i = 0; i < rel->cnt; i++) {
> > +		unsigned long pc = handler + rel->entries[i].offset;
> > +		unsigned long v = rel->entries[i].sym;
>
>                 /* anchor etc. moved into do_reloc_pcalau12i */
>
> > +		union loongarch_instruction *insn =
> > +			(union loongarch_instruction *)pc;
>
>                 switch insn[0]->reg1i20_format->reg1i20_format {
>                 case pcaddu12i_op:
>                         do_reloc_pcaddu12i(insn, pc, v);
>                         break;
>                 case pcalau12i_op: /* TODO: add it for asm/inst.h */
>                         do_reloc_pcalau12i(insn, pc, v);
>                         break;
>                 default:
>                         panic("what the f**k");
>                 }
>
> Alternatively, we can also emit the pcalau12i/addi.d/lu32i/lu52i
> sequence and overwrite the pcaddu12i/ori sequence generated by the old
> toolchain.
>
> Which way do you like?

v3 tested successfully in both new and old toolchains.

Youling.
>